Method of forming a transparent window in a polishing pad

Abstract

The polishing pad for a chemical mechanical polishing apparatus, and a method of making the same. The polishing pad has a covering layer with a polishing surface and a backing layer which is adjacent to the platen. A first opening in the covering layer with a first cross-sectional area and a second opening in the backing layer with a second, different cross-sectional area form an aperture through the polishing pad. A substantially transparent polyurethane plug is positioned in the aperture, and an adhesive material fixes the plug in the aperture.

What is claimed is:  
     
       1. A method of forming a window in a polishing pad, comprising: 
       forming an aperture in a polishing pad, the aperture including a first section with a first cross-sectional dimension adjacent a first surface of the pad and a second section with a second, different cross-sectional dimension adjacent a second surface of the pad opposite the first surface; and  
       securing a transparent plug in the aperture.  
     
     
       2. The method of claim  1 , wherein the first surface of the pad is a polishing surface. 
     
     
       3. The method of claim  2 , wherein securing the transparent plug in the aperture includes placing a top surface of the plug substantially coplanar with the polishing surface. 
     
     
       4. The method of claim  2 , wherein the first dimension is larger than the second dimension. 
     
     
       5. The method of claim  2 , wherein the first dimension is smaller than the second dimension. 
     
     
       6. The method of claim  5 , wherein adhesively attaching the plug includes placing an adhesive on a lip between the first and second sections of the aperture. 
     
     
       7. The method of claim  1 , wherein securing the plug in the aperture includes adhesively attaching the plug to the polishing pad. 
     
     
       8. The method of claim  1 , wherein forming the aperture includes forming the first section of the aperture in a first layer of the polishing pad and forming the second section of the aperture in a second layer of the polishing pad. 
     
     
       9. The method of claim  1 , wherein the plug has a first portion and a second portion, and securing the plug in the aperture includes placing the first portion of the plug in the first section of the aperture and placing the second portion of the plug in the second section of the aperture. 
     
     
       10. The method of claim  1 , wherein the plug includes polyurethane. 
     
     
       11. A method of forming a window in a polishing pad, comprising: 
       forming an aperture through a polishing pad, the aperture including a first section with a first cross-sectional dimension adjacent a polishing surface of the pad and a second section with a second, smaller cross-sectional dimension adjacent a back surface of the pad opposite the polishing surface; and  
       securing a transparent plug in the aperture.  
     
     
       12. A method of chemical mechanical polishing, comprising: 
       bringing a substrate into contact with a polishing surface of a polishing pad that has an aperture formed therein and a transparent plug secured in the aperture, the aperture including a first section with a first cross-sectional dimension adjacent the polishing surface of the pad and a second section with a second, different cross-sectional dimension adjacent a back surface of the pad opposite the polishing surface;  
       causing relative motion between the substrate and the polishing surface;  
       directing a light beam through the transparent plug; and  
       monitoring reflections of the light beam from the substrate.  
     
     
       13. The method of claim  12 , further comprising supplying a polishing slurry to the polishing surface. 
     
     
       14. The method of claim  13 , wherein a top surface of the plug is coplanar with the polishing surface. 
     
     
       15. The method of claim  12 , wherein the polishing surface is attached to a platen, and causing relative motion includes rotating the platen.